This invention relates to wired networks for transmission of data, and particularly relates to cable television (CATV) networks for data transmission.
Cable television (CATV) systems generally comprise a head end facility from which a plurality of trunks or main distribution lines emanate in a hub-and-spoke arrangement. Each trunk serves one or more local distribution networks each of which serves a relatively small number (e.g., about 100 to 250) of end users. Each end user is connected with one of the trunks via a feeder line that taps into the main trunk at a feeder tap location.
As CATV services have expanded from simple unidirectional services in which signals are sent only from the service provider to the end user, but not vice versa, to bidirectional services in which signals are also sent from the end users back to the service provider, the demands for high performance of the cable system have also expanded. In particular, when digital signals are sent from the end users to the service provider, it is important to maintain a low bit error rate for these signals so that the information encoded in the signals is accurately transmitted to the service provider.
One factor that can lead to higher incidence of bit errors in the return path (i.e., the path from the end user to the head end facility) of a cable system is so-called group delay, wherein one or more frequency components of the return signal arrive at the head end facility at a slightly different time than one or more other frequency components that were transmitted by the end user at the same time. Group delay can be introduced into the return path, for example, by diplex filters that are commonly employed in the distribution amplifiers of cable systems for separating the forward and return signals. Amplifiers with diplex filters inherently cause some frequencies to be delayed more or less, by tens or hundreds of nanoseconds, than other frequencies.